The "ghost" interference mica powders that I am using in this video I got from eBay, from this vendor (click the small selection arrow, you will see there sampling kits as a choice, the one I got is the 5g, you can see it's a lot and goes a long way)

Also, for the moment PolyClayPlay is out of stock of Platinum. I got mine from Switzerland, I found an online store that has a decent shipping but it takes about 2 weeks to get it in the US, the store is Buddlycrafts